In a number of applications there is a requirement for the provision of sinusoidal waveform signals to drive the modulation of other signals, or to modify transducer outputs. Sinusoidal waveform signals are selected in a number of instances to minimize the number of harmonic components present in a signal other than its base frequency.
For example, imaging range finding or range imaging applications modulate both a light source for a scene and an imaging transducer with a common modulation frequency. Phase differentials are detected between the output source and received transducer signals to provide an indication as to the range to a particular object in the illuminated scene. An example of this type of image ranging technology is disclosed in the patent specification published as PCT Publication No, WO2004/090568.
Other types of phase sensitive imaging applications have also been developed which require the provision of such modulation signals; such as for example, diffusion tomography, intensity modulated optical spectrometry (IMOS) and fluorescence lifetime imaging (FLM) applications.
The processing algorithms and mathematics employed in such applications often rely on the assumption that the modulation or sampling frequencies used are sinusoidal. However, in practice these expected sine waves are commonly provided by square waves which can be easily generated using off the shelf, low cost digital components.
Square waves include a number of higher order harmonic frequencies in their make up. These high order harmonics can introduce a source of error with respect to measurements of phase completed with respect to such imaging systems.
To address this problem a well known sinusoidal wave generation technique can be used to provide a sine wave from a number of phase separated square waves with varying peak amplitudes. These phase separated square waves are summed together simultaneously, with the number of input square waves used being dictated by the resolution of the sine wave simulation required.
However, this sine wave simulation technique does cause practical difficulties with respect to the physical circuitry required to implement a signal generation apparatus. The resolution of the sine wave provided is directly dictated by the number of square wave generators available, where the provision of a large number of square wave generation signals may not necessarily be practical or cost effective in a number of applications. This approach also necessitates signal use of analogue waveforms, as a result of the summation process.
Furthermore, the summation of several digital signals, comprising of only two voltage levels, generates a signal of multiple voltage levels that is essentially analogue in nature, negating the advantages of digital transducer modulation.
An improved signal simulation apparatus and/or method of simulating signals which addressed any or all of the above problems would be of advantage. In particular a signal simulation system which could provide or approximate an analogue signal with a minimum number of harmonic components using a single square wave generation circuit would be of advantage.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.